U.S. patent number 4,879,539 [Application Number 07/307,524] was granted by the patent office on 1989-11-07 for laminated coil for an eddy-current type strong ac magnetic field generator.
This patent grant is currently assigned to Kanazawa University. Invention is credited to Kazuo Bessho.
United States Patent |
4,879,539 |
Bessho |
November 7, 1989 |
Laminated coil for an eddy-current type strong AC magnetic field
generator
Abstract
The disclosed coil is for a strong AC magnetic field generator
with coaxially laminated eddy-current carrying conductor disks each
of which disks have a central hole and a radial slit. Each turn of
the coil consists of an annular conductor plate disposed between
adjacent disks and each turn is insulated from the adjacent
conductor disks by insulation rings inserted between the annular
conductor plate and the adjacent conductor disks. The annular
conductor plate and the insulating rings in each turn of the coil
have radial slits. The slits in one coil turn are aligned in a
radial direction, but the slits of adjacent coil turns are
angularly displaced with respect to the central hole of the
conductor disk. A slitted end of the annular conductor plate of
each coil turn is connected to that of the immediately neighboring
coil turn through the radial slits of the conductor disk and the
insulation ring.
Inventors: |
Bessho; Kazuo (Kanazawa,
JP) |
Assignee: |
Kanazawa University (Kanazawa,
JP)
|
Family
ID: |
12894282 |
Appl.
No.: |
07/307,524 |
Filed: |
February 8, 1989 |
Foreign Application Priority Data
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Mar 7, 1988 [JP] |
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63-51704 |
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Current U.S.
Class: |
335/299;
335/296 |
Current CPC
Class: |
H01F
7/202 (20130101) |
Current International
Class: |
H01F
7/20 (20060101); H01F 005/00 () |
Field of
Search: |
;335/299,296,300,243,250 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1491786 |
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Sep 1966 |
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FR |
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142508 |
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Aug 1983 |
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JP |
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84103 |
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Apr 1988 |
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JP |
|
229704 |
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Sep 1988 |
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JP |
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Primary Examiner: Harris; George
Attorney, Agent or Firm: Spencer & Frank
Claims
What is claimed is:
1. A laminated coil for an eddy-current type strong AC magnetic
field generator with a plurality of eddy-current carrying conductor
disks, each disk having a central hole and a radial slit extending
from the central hole, said coil comprising a plurality of annular
conductor plates having radial slits respectively, and a plurality
of insulation rings with radial slits respectively, each turn of
the coil being formed of a coaxial lamination of one said annular
conductor plate and at least one said insulation ring with the
radial slits of the annular conductor plate and the insulation
rings being aligned in one radial direction, adjacent turns of the
coil being coaxially laminated one of the other so as to allow
insertion of one said conductor disks therebetween in an insulated
manner, the radial slits of the adjacent turns of the coil being
displaced in circumferential direction in such a manner that a
slitted end of the annular conductor plate of each turn is brought
into contact with the annular conductor plate of an immediately
neighboring turn through the radial slits of said each turn and the
conductor disk.
2. An eddy-current type strong AC magnetic field generator,
comprising a plurality of eddy-current carrying conductor disks,
each disk having a central hole and a radial slit extending from
the central hole; and a coil formed of a plurality of annular
conductor plates having radial slits respectively, and a plurality
of insulation rings with radial slits respectively; each turn of
the coil being formed of a coaxial lamination of one said annular
conductor plate and at least one said insulation ring with the
radial slits of the annular conductor plate and the insulation
rings being aligned in one radial direction, adjacent turns of the
coil being coaxially laminated one on the other so as to have one
said conductor disk inserted therebetween in an insulated manner,
the radial slit of the conductor disk being aligned with that of an
immediately neighboring coil turn, the radial slits of the adjacent
turns of the coil being displaced in circumferential direction in
such a manner that a slitted end of the annular conductor plate of
each turn is brought into contact with the annular conductor plate
of an immediately neighboring turn through the radial slits of said
each turn and the conductor disk immediately below.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a laminated coil for an eddy-current type
strong alternating-current (AC) magnetic field generator which is
suitable for various research works in magnetic properties of
materials such as magneto-optics, in power magnetics, in
bio-magnetics, and in nuclear fusion. More particularly, the
invention relates to a laminated coil of the above type which is
very simple in construction and is easy to manufacture.
2. Overview of the Invention
A laminated coil of the invention is for excitation of an AC
magnetic field generator, and it has a plurality of annular
conductor plates disposed one on the other, and each of the annular
conductor plates has a radial slit. The slitted edge of each
annular conductor is bent toward its adjacent annular conductor
plate and connected thereto, so that a coil made of a continuous
spiral conductor plate is formed by the annular conductor plates
thus connected. One conductor disk with a central hole and a radial
slit extending from the central hole is inserted into each of the
inter-layer space between adjacent annular conductor plates of the
coil, and the conductor disk is insulated from the annular
conductor plates by inserting insulation rings between the opposite
surfaces of the conductor disk and the facing annular conductor
plates. Each insulation ring also has a radial slit. That slitted
edge of each annular conductor plate which is bent toward and
connected to the adjacent annular conductor plate extends through
the radial slits of the conductor disk and the insulation ring.
When an alternating current flows through the laminated coil, an AC
eddy current is induced in each conductor disk in its
circumferential direction. The eddy current flows along the
periphery of the conductor disk except its radial slit, and at the
radial slit the eddy current flows along the slitted edge and the
peripheral edge of the central hole of the conductor disk. Thus,
the density of the eddy current becomes very high along the
peripheral edge of the central hole, and a highly concentrated
magnetic flux can be induced in the central hole of the conductor
disk. In short, with the large AC exciting current, a strong AC
magnetic field can be generated in the central hole of the
conductor disk. The laminated coil of the above structure is
characterized in that its impedance is very low, and a very large
exciting current can be fed through it. Accordingly, a very high
concentration of eddy currents can be produced along the edge of
the central hole of each conductor disk, so that a strong AC
magnetic field can be generated efficiently in the central hole.
Further, the above-mentioned laminated coil is very easy to
manufacture. Related Art Statement
Much efforts are currently undertaken for research and development
of strong magnetic field generators by using large-scale
experimental facilities, in order to promote investigations and
studies of properties of materials in strong magnetic field,
preparation and testing of new materials and experiments on nuclear
fusion.
Conventional strong magnetic field generators can be classified
into several groups; namely, destructive pulse strong magnetic
field generators such as those of KNER method and the implosion
method, nondestructive pulse strong magnetic field generators such
as those of the multilayered coil type and the so-called MIT type,
continuous strong magnetic field generators such as those of
superconductive type and hybrid type.
The strong magnetic field generators of the prior art provide very
strong magnetic fields, but they have shortcomings in that the
duration of the strong magnetic fields generated is very short,
that special facilities such as extremely low temperature apparatus
and large power source apparatus are required, that only pulse or
direct-current (DC) magnetic field can be generated, and that
continuous generation of strong alternating-current (AC) magnetic
field is not possible. On the other hand, the study of
bio-magnetics has particularly advanced, and the need for
investigation of the relation between the living body and AC
magnetic field has increased, so that there is a demand for the
development of a strong AC magnetic field generator.
To overcome the above shortcomings of the prior art, the inventors
have disclosed a variety of strong AC magnetic field generators in
their Japanese Patent Applications No. 57-25,517 and No.
61-228,459, and recently they have disclosed
multilayered-eddy-current type strong AC magnetic field generators
in their Japanese Patent Application No. 62-62,708 and No.
62-188,921. FIG. 4A and FIG. 4B show eddy-current type AC magnetic
field generators which were disclosed by the inventors recently.
When an AC current is fed into exciting coils of the magnetic field
generator, eddy currents are induced in electric conductors which
are magnetically coupled to the coils, and the conductors are
connected to such a common central hole that the induced eddy
currents are concentrated along the periphery of the central hole.
Thereby, the AC magnetic flux density along the central hole is
efficiently increased while minimizing the leakage flux.
More specifically, a conductor disk 11 of FIG. 4A has a central
hole 12 and branch conductors 13a through 13d in the form of
concentric cylindrical walls perpendicular to the plane of the disk
11. The conductor disk 11 of FIG. 4B is similar to that of FIG. 4A
except that its branch conductors 13a through 13d are in the form
of annular conductors parallel to the plane of the disk 11. In both
examples of FIGS. 4A and 4B, the conductor disk 11 has a radial
slit 14 extending from its central hole 12 to its periphery through
all the branch conductors 13a through 13d. Exciting coils 15a
through 15c are inserted in the three spaces between adjacent walls
of the four branch conductors 13a through 13d as shown in the
figures.
With an AC exciting current in each of the exciting coils 15a, 15b
and 15c, an eddy current is induced in each of the branch
conductors 13a, 13b, 13c and 13d in the circumferential direction
thereof. Due to the presence of the radial slit 14, the path of the
eddy current in each branch conductor is closed along the opposite
edges of the radial slit 14 and the periphery of the central hole
12. Accordingly, the eddy currents of the individual branch
conductors are all led to the periphery of the common central hole
12. Thus, a concentrated high magnetic flux is induced in the
central hole 12, and it becomes possible to generate continuously a
strong AC magnetic field within the central hole 12.
However, the multilayered-eddy-current type strong AC magnetic
field generators which were proposed heretofore have the following
shortcomings; namely, that they are difficult to manufacture
because the conductor disk with branches has a complicated shape
and the exciting coils consist of windings, and that the intensity
of the magnetic field to be generated thereby is limited at a
comparatively low level because the exciting coil of the proposed
type inherently has a high inductance and the conductors of the
proposed structure are inherently affected by surface effects.
Thus, the multilayered eddy-current type strong AC magnetic field
generators of the prior art still have serious problems to be
solved.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is the solve the
above-mentioned problems of the prior art by providing a laminated
coil for eddy-current type strong AC magnetic field generators. A
coil for eddy-current type strong AC magnetic generator according
to the invention has simple construction and is easy to
manufacture, and when it is used as an exciting coil its impedance
is low, and it suits to thin low-surface-effect conductors for
carrying eddy currents. Thus, the coil of the invention enables
considerable increase of the intensity of magnetic field to be
produced by such AC magnetic field generators.
A laminated coil according to the invention is for an eddy-current
type strong AC magnetic field generator with a plurality of
eddy-current carrying conductor disks, each of which disks has a
central hole and a radial slit extending from the central hole. The
laminated coil comprises a plurality of annular conductor plates
having radial slits respectively, and a plurality of insulation
rings with radial slits respectively. The radial slit of each
insulation ring preferably has a wider opening than that of the
annular conductor plate. Each turn of the coil is formed of a
coaxial lamination of one of the annular conductor plates and at
least one of the insulation rings with the radial slits of the
conductor plates and the insulation rings aligned in a radial
direction. The adjacent turns of the coil are coaxially laminated
one on the other so as to allow insertion of one of the conductor
disks therebetween in an insulated manner. The radial slits of the
adjacent turns of the coil being displaced in circumferential
direction in such a manner that a slitted end of the annular
conductor plate of each turn is brought into contact with the
annular conductor plate of the immediately neighboring turn through
the radial slits of the insulation ring and the conductor disk.
When the eddy-current type strong AC magnetic field generator is
provided with and excited by the above-mentioned laminated coil of
the invention, eddy currents are induced in the conductor disks and
such eddy currents are concentrated along the periphery of the
central holes of the individual disks, so that highly intensified
magnetic field can be generated in the holes. Besides, the
structure of the laminated coil is very simple and it can be
produced at a much lower cost than before, yet it enables a
considerable increase in the strength of the magnetic field to be
generated by the AC magnetic field generator.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention, reference is made to
the accompanying drawings, in which:
FIGS. 1A, 1B and 1C diagrammatically illustrate examples of
essential elements of a laminated coil of the invention, i.e., a
conductor disk for carrying eddy current, an annular conductor
plate and an insulation ring respectively;
FIG. 2 is an explanatory diagram of the manner in which annular
conductor plates of a laminated coil and conductor disks of an
eddy-current type AC magnetic field generator are assembled in an
embodiment of the invention;
FIG. 3 is a schematic diagram showing the current in the exciting
coil and the eddy current induced in the conductor disk of the
eddy-current type AC magnetic field generator; and
FIGS. 4A and 4B are partially cut away perspective views of
conventional multilayered-eddy-current type AC magnetic field
generators, respectively.
Through different views of the drawings, the followed symbols are
used.
1, 1a, 1b: thin conductor disks,
2: a central hole,
3, 5, 7: radial slits,
4, 4a, 4b, 4c: annular conductor plates,
6: an insulation ring,
8: a cylindrical assembly,
9, 9a, 9b, 9c: alternating currents,
10, 10a, 10b: eddy currents,
11: a conductor disk,
12: a central hole,
13a through 13d: branches,
14: a slit,
15a through 15c: coils.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention will be described now in further detail by referring
to embodiments shown in the drawings.
With the present invention, a laminated coil or an exciting coil
for inducing eddy currents is formed by using a continuous spiral
conductor plate, and a thin conductor disk 1 with a central hole 2
and a radial slit 3 extending from the central hole 2 to its
periphery is inserted in each of the inter-turn space of the
exciting coil while insulating the conductor disk from the exciting
coil. In response to the application of an alternating current to
the laminated coil, alternating eddy currents are induced in the
thin conductor disks 1 so as to produce a strong AC magnetic field
through the central holes 2 of the conductor disks 1.
To facilitate the manufacture of the continuous spiral conductor
plate of the laminated coil, individual turns of the coil are at
first made in the form of separate annular conductor for plate 4.
Such annular conductor plates 4 are coaxially overlaid one over the
other so as to form a cylindrical assembly 8. Slitted edge of each
annular conductor plate 4 is bent toward the immediately
neighboring annular conductor plate 4 and connected thereto. The
desired continuous spiral conductors plate can be completed by
successively repeating the above bending and connecting of the
individual annular conductor plates 4 to that of the adjacent turns
in succession.
More specifically, each thin conductor disk 1 has a central hole 2
and a radial slit 3, which slit 3 extends from the central hole 2
to the periphery of the disk 1 as shown in FIG. 1A. Preferably, the
radial slit 3 of the conductor disk 1 is of sector shape with its
opening becoming increasingly larger as it approaches to the
periphery. The annular conductor plate 4 for the exciting coil has
a radial slit 5 which preferably has narrowly spaced parallel edges
as shown in FIG. 1B. The insulation ring 6 for insulating the
conductor disk 1 from the conductor plate 4 of the exciting coil is
preferably in the form of an annular insulator with a radial slit 7
of sector shape as shown in FIG. 1C. The shape and the size of the
insulation ring 6 of FIG. 1C can be similar to those of the annular
conductor plate 4 of FIG. 1B except that the radial slit 7 of the
insulation ring 6 is wider than the radial slit 5 of the conductor
plate 4.
To make the laminated coil for the eddy-current type strong AC
magnetic field generator, the annular conductor plates 4 and the
thin conductor disks 1 are alternatively overlaid one over the
other while aligning the slits 5 and 3 of neighboring conductor
plate 4 and the disk 1 as shown in FIG. 2. The insulation rings 6
(not shown in FIG. 2) are inserted between each conductor disk 1
and its adjacent annular conductor plates 4 while aligning the
radial slits 7 of the insulation ring 6 with the slits 3 of the
conductor disks 1. Thus, a cylindrical assembly 8 is formed as
shown by dash-dot lines of FIG. 2. Three annular conductor plates
4a, 4b, 4c and two conductor disks 1a and 1b are shown in the
cylindrical assembly 8.
One slitted edge of, for instance, the annular conductor plate 4a
is bent toward the immediately neighboring annular conductor plate
4b through the radial slits 3a and 7 (not shown) of the conductor
disk 1a and the insulation ring 6 (not shown), so that the bent
edge of the conductor plate 4a is connected to the neighboring
conductor plate 4b. Similarly, one slitted edge of each of the
remaining annular conductor plates 4b, 4c, . . . is bent toward and
connected to the immediately neighboring annular conductor plates
4c, 4d (not shown), . . . , respectively. Thereby, a continuous
spiral conductor plate for the exciting coil is formed. For a
desired intensity of the AC magnetic field, the necessary number of
the eddy-current-carrying thin conductor disks 1 is determined, and
the thus determined number of the conductor disks 1 are assembled
together with the corresponding number of the annular conductor
plates 4 in the form of the cylindrical assembly 8 of FIG. 2.
When the exciting coil of the spirally connected conductor plates
4a, 4b, 4c, . . . is connected to an AC power source to feed an AC
electric current thereto as shown by currents 9a, 9b, 9c, . . . of
FIG. 3, eddy currents 10a, 10b, . . . are induced in the thin
conductor disks 1a, 1b, . . . in their peripheries adjacent to the
conductor plates 4a, 4b, 4c, . . . In each conductor disk 1, such
eddy current is induced in the circumferential direction thereof,
and due to the presence of the radial slit 3, the path of the eddy
current induced along the periphery is closed along the opposing
edges of the radial slit 3 and the peripheral edge of the central
hole 2, so that the current density at the periphery of the central
hole 2 is high. In the example of FIG. 2, if the exciting currents
9a, 9b, 9c flow in the clockwise direction in the annular conductor
plates of the laminated coil, the eddy currents 10a, 10b are
induced in the counter-clockwise direction at the outer
circumference of the conductor disks, and such eddy currents flow
in the clockwise direction along the periphery of the central holes
2 of the conductor disks.
Thus, the density of the eddy current becomes high along the
periphery of the central hole 2 of each conductor plate 1, so that
a high AC magnetic flux density is induced in the inside of the
central hole 2. Besides, the magneto-motive forces in the central
holes of all the individual conductor disks 1 are generated in the
same direction in a cumulative fashion, so that the resultant
magnetic flux in the central hole 2 is further intensified by the
cumulative effects of the eddy currents in the plurality of
conductor disks 1. Thus, an extremely high intensity of the
magnetic field can be achieved at the central hole 2.
As described in detail in the foregoing, although an eddy-current
type strong AC magnetic field generator which is equipped with the
laminated coil according to the present invention generates a
strong AC magnetic field based on the same operating principle as
that of the conventional multilayered-eddy-current type strong AC
magnetic field generators of FIGS. 4A and 4B, the present invention
considerably simplifies the structure of such magnetic field
generator and makes its production much easier. Furthermore, the
following effects can be achieved.
(1) A magnetizing coil with that number of turns which is necessary
for generating a required intensity of the magnetic field can be
formed simply by laminating the number of annular conductor
plates.
(2) The use of one continuous spiral conductor plate to form the
exciting coil for the induction of eddy currents results in a very
low impedance of the exciting coil, so that a large exciting
current can be applied to such coil so as to induce a strong eddy
current, and a very high magnetic flux density can be generated.
Besides, such strong eddy currents in a number of conductor disks
can produce cumulative magnetomotive forces, so that an extremely
strong AC magnetic field can be generated.
(3) Due to the structural simplicity of the exciting coil and the
eddy-current types strong AC magnetic field generator, special
alloys with a high mechanical strength such as copper alloys can be
used in the exciting coil conductors and the eddy-current-carrying
conductors. Further, laminated structure made of such strong alloys
can be cooled by a simple cooling system. In short, the structural
simplicity provided by the present invention results in a number of
advantages of the strong AC magnetic field generators.
(4) The exciting coil of the invention can be energized by an AC
power source of variable frequency, so that it facilitates the
production of a variable frequency type strong AC magnetic field
generator. In addition, a pulse type strong AC magnetic field
generator can be formed simply by driving the exciting coil by a
pulse power source.
Although the invention has been described with a certain degree of
particularly, it is understood that the present disclosure has been
made only by way of example and that numerous changes in details of
construction and the combination and arrangement of parts may be
resorted to without departing from the scope of the invention as
hereinafter claimed.
* * * * *